A process of drug absorption by which cells carry a drug across their membrane by engulfing the drug particles is known as:

• A. Active absorption
• B. Passive absorption
• C. Transcytosis
• D. Pinocytosis

Answer: (D)

Engulfing drug particles by the cell membrane describes pinocytosis, a form of endocytosis often called cellular drinking. In pinocytosis, the membrane folds inward to form vesicles that pinch off inside the cell, capturing extracellular fluid and solutes, including drug particles. This process requires energy and moves substances into the cell rather than across it in one step. It differs from passive diffusion or carrier-mediated active transport, which rely on gradients or specific transporters. It also differs from transcytosis, which emphasizes moving material from one side of an epithelial cell to the other after endocytosis. So the mechanism described is pinocytosis.